This disclosure is related to block copolymers, methods of manufacture thereof and to articles comprising the same. In particular, this disclosure is related to block copolymers used for improved nanolithography patterning.
Modern electronic devices are moving toward utilization of structures that have a periodicity of less than 40 nanometers (nm). The ability to shrink the size and spacing of various features on a given substrate (e.g., gates in field effect transistors) is currently limited by the wavelength of light used to expose photoresists (i.e., 193 nm). These limitations create a significant challenge for the fabrication of features having a critical dimension (CD) of less than 40 nm.
Block copolymers have been proposed as one solution to formation of patterns with periodicity of less than 40 nanometers. Block copolymers form self-assembled nanostructures in order to reduce the free energy of the system. Nanostructures are those having average largest widths or thicknesses of less than 100 nanometers. This self-assembly produces periodic structures as a result of the reduction in free energy. The periodic structures can be in the form of domains, lamellae or cylinders. Because of these structures, thin films of block copolymers provide spatial chemical contrast at the nanometer-scale and, therefore, they have been used as an alternative low-cost nano-patterning material for generating periodic nanoscale structures.
Many attempts have been made to develop copolymers and processes for patterning. FIGS. 1A and 1B depict examples of lamella forming block copolymers that are disposed upon a substrate. The block copolymer comprises a block A and a block B that are reactively bonded to each other and that are immiscible with each other. The alignment of lamellae domains can be either parallel (FIG. 1A) or perpendicular (FIG. 1B) to the surface of a substrate surface upon which they are disposed. The perpendicularly oriented lamellae provide nanoscale line patterns, while there is no surface pattern created by parallel oriented lamellae.
Where lamellae form parallel to the plane of the substrate, one lamellar phase forms a first layer at the surface of the substrate (in the x-y plane of the substrate), and another lamellar phase forms an overlying parallel layer on the first layer, so that no lateral patterns of microdomains and no lateral chemical contrast form when viewing the film along the perpendicular (z) axis. When lamellae form perpendicular to the surface, the perpendicularly oriented lamellae provide nanoscale line patterns. Cylinder forming block copolymers, on the other hand, provide nanoscale line patterns when the cylinders form parallel to the surface and hole or post patterns when the cylinders form perpendicular to the surface. Therefore, to form a useful pattern, control of the orientation of the self-assembled microdomains in the block copolymer is desirable.
Directed Self-Assembly (DSA) of block copolymers is one method of advanced patterning technologies that enable sub-10 nm technology nodes. One of the leading DSA processes, chemoepitaxy, involves a chemical pattern to align lamellar block copolymer morphologies. Poly(styrene-block-methyl methacrylate) (PS-b-PMMA) has been widely studied in DSA using chemoepitaxy to demonstrate the potential of DSA to extend optical lithography. However, the relative weak segregation strength (low Flory-Huggins interaction parameter χ) and weak etch selectivity of PS-b-PMMA limits its capability to pattern small features (less than 11 nm) with low line edge roughness (LER) and effective pattern transfer. Block copolymers with stronger segregation strength (high χ) and higher etch selectivity may be useful at sub-10 nm nodes. The main challenges in developing formulations and processes for high χ lamellar block copolymer lie in the mismatched surface energies between the two blocks at the air interface, which drives the lamellae to align parallel (FIG. 2B) rather than perpendicular (FIG. 2A) to the substrate. A few approaches have been developed to overcome the unbalanced surface energy of high χ materials in DSA, such as using external fields (e.g., electrical, magnetic or mechanical).
Solvent evaporation in conjunction with an electrical field is one way of applying an external field to direct the block copolymer to align perpendicular to the substrate. Another method of directing alignment in block copolymers includes physically placing a layer of neutral material on top of the block copolymer, or spin coating a polarity switching top coat that is neutral to both blocks during thermal annealing. It is difficult however, to incorporate and reproducibly control the external alignment fields or physical placement (of the top layer) on track in industrial scale fabrication, while the polarity switching top coat cannot withstand the high annealing temperature (greater than 200° C.) to satisfy the high throughput requirement (within minutes of thermal annealing) in semiconductor industry.
It is therefore desirable to find block copolymers that can generate self-assembled films having domain sizes of less than 25 nanometers with a periodicity of less than 50 nanometers. Additionally, it is desirable to find block copolymers that contain highly etch resistant domains that can deliver low defects at 50 nm or less pitch under thermal annealing processes without a metal staining process, as this would save additional expensive processing steps and should lead to lower (better) line width roughness.